Variable resistance without contacts



3, 1950 c. B. FOWLER 2,517,553

VARIABLE RESISTANCE wrmou'r CONTACTS Filed Oct. 26, 1945 2 Sheets-Sheet1 Qmwm CLARENCE B. FOWLER MWLW altar/nu;

3, 1950 c. B. FOWLER VARIABLE RESISTANCE WITHOUT CONTACTS 2 Sheets-Sheet2 Filed QOt. 26, 1945 Ema/WM 3 CLARENCE a. FOWLER Patented Aug. 8, 1950VARIABLE RESISTANCE WITHOUT CONTACTS Clarence B. Fowler, Washington, D.C.

Application October 26, 1945, Serial No. 624,916

4 Claims. (Cl. 172-36) (Granted under the act of March 3, 1883, asamended April 30, 1928; 370 0. G. 757) My invention relates toelectrical conductors and more particularly to electrical conductorsadapted to change current flow without the use of moving contacts.

One of the principal disadvantages of the use of electricity is the flrehazard, wear, radio interference, and maintenance associated with movingcurrent carrying contacts. This is particularly significant in the caseof direct current systems where motors, generators, and inductiondevices require commutating mechanisms to provide reversal of current.In the case of D.-C. motors designed for hazardous locations thenecessity of a commutator has required special motor structural designhaving airtight enclosures. In the case of motors designed for use onaircraft, the need for a commutator has caused considerable difllcultyby reason or the loss of commutator finish at high altitudes. Thisproblem has not yet been satisfactorily solved.

I have discovered that the above mentioned disadvantages of electricalcommutators or switches can be avoided by the use of a resistancecomprising a conducting liquid enclosed in a flexible tube. By mountingthe ends of the tube in a solid housing and providing for a change inthe pressure of the liquid within the tube, I am enabled to vary theresistance between the two ends without moving contacts of any type. Ithereby achieve a variable resistance which is inherently safe for usein hazardous locations and which does not have the high maintenance andlow reliability incident to the use of moving contacts.

In accordance with another aspect of my invention, my variableresistance is connected in a bridge circuit whereby a variable voltageor a variable current is obtained from a constant direct voltage source.This enables me to obtain an alternating current from a direct currentsource without the use 01' moving contacts of any kind.

In accordance with a further aspect of my invention the pressure of theliquid within my variable resistance is varied in accordance with theangular position of a shaft and the magnitude and direction of currentapplied to a motor thereby changed in accordance with shaft position. Itherefore am enabled to produce a direct current motor without movingcurrent carrying contacts.

Further, in accordance with my invention, my variable resistance ismounted on a helical core, thereby obtaining a variable magnetomotiveforce in accordance with the liquid pressure in the resistance. I

In accordance with a further aspect of my invention, a resistance whichvaries in accordance with the current is achieved by using a helixcomposed of my variable resistance wound about a movable magnetic rodwhich in turn varies the liquid pressure within my resistance tube.

While my invention is susceptible of various modifications andalternative constructions, I have shown in the drawings and will hereindescribe in detail the preferred embodiments. It is to be understood,however, that I do not intend to limit the invention by such disclosurefor I aim to cover all modifications and alternative constructionsfalling within the spirit and scope of the invention as defined in theappended claims.

In the drawings:

Figure 1 shows a cross-sectional view of my invention with theresistance at low liquid pressure.

Figure 2 shows a cross-sectional view of my invention at high liquidpressure.

Figure 3 shows a Wheatstone bridge circuit by which my resistor isenabled to cause a variation in the magnitude and direction of currentflow.

Figure 4 shows a plan view and partial crosssection of a motor adaptedto utilize my resist- Figure 5 shows an axial cross-section of the camused in the motor of Figure 4.

Figure 6 shows a current sensitive solenoid utilizing my invention.

Referring now to Figure 1. Tube l comprises a flexible tube constructedof expansible rubberlike material having end pieces 2 connected thereto.The end pieces 2 are of solid material having a chamber in liquidconnection to the inner portion of tube I. Contact members 3 are mountedwithin the rigid members 2 which may be securely anchored to anysuitable stationary support thereby fixing the distance between thesemembers. As a means of controlling liquid pressure, bulb 4 of flexiblematerial is connected to one end 2. The complete structure is filledwith a conducting liquid such as mercury.

Figure 1 shows the variable resistance for the low pressure, highresistance, condition wherein tube l is unflexed and the cross-sectionof liquid 5 is small throughout the entire length of the tube. Figure 2shows my variable resistor for the high pressure, low resistance,condition. In this case bulb 4 is nearly collapsed while flexible tube Ihas become much thicker. The average area of the conductor 5 throughoutthe length of the tube I in this case is much greater than as shown inFigure l and a correspondingly smaller value of resistance is producedbetween conductors 3.

It will be evident to those skilled in the art that any method ofvarying the pressure within tube i will act to vary the resistance orthe complete unit. As shown in Figures 1 and 2 a bulb is utilized iorthis purpose by reason of its convenience for hand operation. Othermethods, such as a mechanical pump or a bellows, may be used.

Referring now to Figure 3 which shows a method whereby my variableresistance may be used to generate alternating voltage from any suitabledirect current source, such as for example the battery 9, connected topoints AB oi Wheatstone bridge ACBD and the load circuit I2 connected topoints C and D; The Wheatstone bridge consists of bridge arms 6, I, 8,and It.

The bridge ar-m AD consists of variable resistance ll constructed inaccordance with the above discussed principles and actuated by bulb ll.When the ratio of the resistance of IO to resistance 8 is greater thanthe ratio of resistance 6 to resistance I, current flow through load |2will flow in the same direction as when load I2 is connected to points Aand B of the bridge, point D being connected to point B and point Cbeing connected to point A. On the other hand, if the resistance I! tothat of resistance 8 is less than the ratio of resistance 6 toresistance 1 the direction of current fiow through-load l2 will be inthe opposite direction. Hence, by varying the pressure in resistance ID(by operation of bulb I) the direction and magnitude of current flowthrough load I? is changed.

As an alternative to the construction shown in Figure 3, a secondvariable resistance constructed in accordance with my invention may beplaced in bridge arm of C-B of Figure 3 in place oi fixed resistance I.If the bridge is balanced with the two variable resistances in thecondition of no pressure, pressing the bulb of one resistance ofresistor I3 is such that the ratio of resistance will cause current flowthrough load I2 in one direction and pressing the other bulb will causecurrent to flow through load l2 in the opposite direction.

Figure 4 shows in a partial cross-section the plan of a direct currentmotor utilizing the principles of my invention. In the figure, H is ashaft, 25 is a cam connected thereto and I6 is the rotor of the motor.The latter element may comprise a group of permanent magnets. Elementsl5 and." are field poles for the motor having coils H and I9respectively. A magnetic structure (not shown) connects these poles inthe usual manner. These coils comprise flexible resistance elements suchas shown in Figure 1 except that they are mounted about the poles toproduce magnetomotive force when current flow takes place. Coils I4 andI9 are connected to batteries l3 and 20 respectively. The liquid incoils I4 and I3 is contained within the coils themselves and todiaphragms 2| and 22 respectively so that pressure on either of thesediaphragms alters the resistance of the corresponding coils. Members 23and 24 coact with cam 25 to press diaphragms 22 and 2| respectively sothat for every position of cam 25 there is a corresponding position ofthe two diaphragms, pressure in the two coils, resistance of the twocoils, and magnetomotive force in the magnetic structure. I

Figure 5 is an axial section of my motor as shown in Figure 4. The cam25 is shown as an elliptical section although other shapes may be used.Guides 25 and 21 control the motion of members 24 and 23 respectively sothat rotation of cam 25 alternately increases the pressure withindiaphragms 2| and 22.

When cam 25 is in a position such that dia- 4 phragms 2| and 22 arecompressed to an equal degree, the resistance of coil I4 is equal to theresistance oi coil l9 and equal currents from batteries I 3 and 20 flowthrough the two coils. In this case the magnetomotive force from coil I4is equal and opposite to the magnetomotive force of coil l3 and no fluxis produced in the magnetic structure by these coils. On the other hand,when cam 25 is in a position such that diaphragm 22 is compressed anddiaphragm 2| permitted to expand, coil It has a higher resistance thancoil l9 and a correspondingly greater magnetomotlve force is produced bycoil l9 than by coil ll. In this case a net magnetomotive force actsthrough the magnetic circuit and flux is produced, thereby causingrotation of rotor l6. Ii. the cam 25 causes diaphragm 2| to becompressed to a greater degree than diaphragm 22, the reverse actiontakes place and more current flows through coil ll than coil I9. In thiscase the magnetomotive force of coil ll exceeds that of coil l9 and aflux in the opposite direction is produced. This causes a correspondingrotation oi rotor It.

By shaping cam 25 in accordance with the disposition of the magnets onrotor l6 and poles l5 and I8, I am enabled to cause changes inmagnetomotive force which produce flux always acting to cause rotor IEto turn in a desired direction. The motor then always rotates in thesame direction and, by proper proportioning of cam 25, it is possible tocause a uniform motor torque.

It is evident that the operation of my motor as shown in Figures 4 and 5is accomplished without the use of sliding contacts of any kind. Theentire system is hermetically sealed and introduces no possibility ofsparking. Furthermore, the absence of sliding current carrying contactsavoids the problems associated with the use of commutators at highaltitudes.

An embodiment of my invention for use as a current sensitive resistanceis shown in Figure 6. In the figure, cofl 30 comprises a tube offlexible material similar to that of Figure 1. End connections 28 and 29of coil 30 constitute the terminals of the resistance. End 29 of cofl 3Bis connected by passage 36 to reservoir 33 and reservoir 33 is connectedto diaphragm 3|. Plunger 31 is a permanent magnet adapted to compressdiaphragm 3| in accordance, with the flux produced by coil 30.

Operation of my device as shown in Figure 6 is as follows:

Figure 6 thereby achieves a resistance which decreases in value withcurrent flow in one direction but is constant in value as to currentflow in the reverse direction. a

The invention described herein may be made and used by or for theGovernment of the United States for governmental p rp ses without thepayment to me of any royalties thereon or there- My invention is capableof wide variation from the forms illustrated and described, its scopebeing defined in the appended claims.

I claim:

1. In an electric motor, a shaft, a magnet pole, a coil wound about saidpole, said coil comprising a tubular expansible container of fixedlength, conducting liquid substantially filling said container, adiaphragm-operated pressure chamber in liquid connection with saidcontainer and a cam means on said shaft actuating said diaphragm.

2. A current sensitive resistance comprising a coil composed of atubular expansible container containing an electro-conducting liquid,voltage terminals closing the ends of said coil, a permanent magnetcontained within said coil and in operative engagement with anexpansible diaphragm and a reservoir mounted at one end of said magnetand in liquid connection with each other and with said coil, wherebysaid resistance is adapted to decrease in value with current flow in onedirection and to remain constant in value with current fiow in thereverse direction.

3. In an electric motor, the combination of a shaft, a rotor on saidshaft, a cam secured to said shaft, a pair of field cores ondiametrically opposite sides of said rotor, a tube of predeterminedfixed length arranged in a coil about each of said cores, end piecesclosing the ends of said tubes, a source of electrical energy connectedacross the end pieces of each said tubes for supplying currenttherethrough, a pair of variable pressure chambers on diametricallyopposite sides of said cam, conduit means between each said pressurechamber and an end piece, respectively, of said tubes,electro-conductive material substantially filling said pressurechambers, conduit means, tubes and end pieces, and cam followers betweensaid cam and said variable pressure chambers for alternately varying theeflective volume of said chambers, to thereby cause variations in thecross sectional area of said coils for alternately varying the fluxdensity through said cores thereby obtaining a resultant thrust torotate said rotor.

4. In an electric motor, the combination of a shaft, a rotor on saidshaft, a pair of field cores on diametrically opposite sides of saidrotor, an elongated container of predetermined fixed length arranged ina coil about each of said cores, a source of electrical energy connectedacross each of said containers for Supplying current therethrough, apair of variable pressure chambers each having a diaphragm, conduitmeans between each of said pressure chambers and each of said coils,electro-conductive material substantially filling said pressurechambers, conduit means and containers, and means driven by said shaftfor alternately actuating each of said diaphragms.

CLARENCE B. FOWLER.

' REFERENCES crrEn The following references are of record in the file ofthis patent: 1

UNITED STATES PATENTS Number Name Date 1,428,834 Bjerre Sept. 12, 19221,748,927 Kramer Feb. 25, 1930 2,061,863 Wells Nov; 24, 1936 2,131,758Rypinski Oct. 4, 1938 2,164,728 Wey July 4, 1939 2,316,008 Ludbrook Apr.6, 1943 2,359,085 Chubb Sept. 26, 1944 2,391,966 Harrison Jan. 1, 1946FOREIGN PATENTS Number Country Date 70,025 Germany July 28, 1923

